In wind power plants with a horizontal axial and three rotor blades, the rotational speed above the rated wind speed is regulated by synchronous adjustment of the blade angles in such a way that changing the pitch angle causes the aerodynamic lift and therefore the driving torque to be changed in such a way that the plant is kept within the range of the rated rotational speed. At wind speeds above the switch-off speed, this blade adjustment mechanism is also used as a brake by virtue of the fact that the blades are positioned into the wind with the nose, with the result that the rotor no longer supplies any appreciable driving torque.
During this collective blade adjustment, pitching moments and yawing moments acting on the rotor are produced owing to asymmetric aerodynamic loads. The asymmetric loads arise, for example, as a result of wind shear in the vertical and horizontal directions, owing to boundary layers, as a result of the imprecise orientation of the wind power plant in the wind, gusts and turbulence or as a result of accumulation of the flow at the tower. In order to reduce these asymmetric aerodynamic loads, the pitch angle of the blades can be adjusted individually (Individual Pitch Control, IPC).
WO 2008/041066 A1 is concerned with controlling a rotor load of a wind turbine. In this context, the fore-aft oscillation, that is to say the oscillation in the direction of the wind, can be damped by collective pitching, during which process attempts are made to avoid generating any symmetrical blade oscillation.
DE 297 15 249 U1 describes a wind power plant having a rotor and at least one rotor blade which is mounted on the rotor so as to be rotatable about its longitudinal axis. In order to adjust a rotor blade angle, an adjustment device is provided which is configured to reduce a yawing moment and/or pitching moment which is applied to the rotor.